Three-axis magnetic sensor

ABSTRACT

A three-axis magnetic sensor apparatus is described that is processed together into a single chip, with high performance, low cost, as well as small size. The three-axis magnetic sensor apparatus include a substrate, a two-axis magnetic sensing structure and a single-axis sensing structure. The two-axis sensing magnetic structure consisting of two shielded Wheatstone bridge configurations in conjunction with an annular or semi annular magnetic flux-guiding structure, and the single-axis sensing structure consisting of a push-pull Wheatstone bridge in conjunction with a flux guide that is capable of generating a fringe field whose horizontal component is proportional to the vertical component of an external magnetic field. The two-axis magnetic sensing structure and the single-axis structure are processed together into a single chip, and can be used to measure respectively X, Y and Z components of external magnetic fields.

CROSS REFERENCE OF RELATED APPLICATION

This is a U.S. National Stage under 35 U.S.C 371 of the InternationalApplication PCT/CN2018/111130, filed Oct. 22, 2018, which claimspriority under 35 U.S.C. 119(a-d) to CN201810652651.7, filed Jun. 22,2018; and CN201820970160.2, filed Jun. 22, 2018.

BACKGROUND OF THE PRESENT INVENTION Field of Invention

The present invention belongs to the technical field of magneticsensors, and relates to a three-axis magnetic sensor.

Description of Related Arts

Giant magnetoresistance (GMR) effect is discovered in magneticmultilayer films by Albert Fert and Peter Grünberg, independently, in1988. The GMR sensor has advantages of higher sensitivity, lower powerconsumption, and better linearity as compared to anisotropicmagnetoresistance (AMR) sensors and Hall sensors. In addition, GMRsensors are easy to be integrated with semiconductor circuits, and areconsidered to be one of the best candidates as small size, low power,high performance magnetic sensors.

At present, the technology of three-axis magnetic sensors usuallyencapsulates three dies of single-axis magnetic sensors into the samepackage, in which three dies are arranged in the directions that canseparately measure the magnetic field components along X axis, Y axisand Z axis. However, this technology has several drawbacks includingcomplex packaging process, large package size, and high cost. Forexample, the patent with a publication number of CN102426344B uses adesign that encapsulates three identical sensor dies where two of thedies are placed in the X-Y plane with the sensitive axes respectivelyalong the X-axis and Y-axis, while the other die is placed vertically tothe X-Y plane for the purpose of measuring the Z axis component of theexternal magnetic field. A patent with an application number ofUS20120299587A1 uses a two-axis magnetoresistive sensor to measurerespectively X- and Y-components of external magnetic field, and uses aHall sensor to measure Z-component of external magnetic field. Thepatent US20150309125A1 is to deposit and pattern a plurality of magneticsensing elements on the slopes created by the MEMS technology on thesubstrate, and a magnetic field can be measured by the sensing units,and calculated by a simple algorithm as an expression of measurementvalues and slope angles of the sensing unit.

However, the above-mentioned techniques have the drawbacks includingcomplex device process, difficult packaging process, and largesensitivity variation along X, Y and Z directions.

This invention will overcome the drawbacks regarding to theabove-mentioned techniques, and lead to a low cost, highly integratedand single-chip three-axis magnetic sensor.

SUMMARY OF THE PRESENT INVENTION

An aim of the invention is to provide an integrated three-axis magneticsensor.

The invention comprises a substrate, a two-axis magnetic sensingstructure consisting of two Wheatstone bridge configurations inconjunction with an annular or semi annular magnetic flux-guidingstructure, and another single-axis sensing structure consisting of apush-pull Wheatstone bridge in conjunction configuration with a fluxguide that is capable of generating a fringe field whose horizontalcomponent is proportional to vertical component of a magnetic field.

The two-axis magnetic sensing structure with two Wheatstone bridgeconfigurations and a single-axis structure with a push-pull Wheatstonebridge configuration are processed together into a single chip, and isfor measuring respectively an X-component, a Y-component and a Zcomponent of an external magnetic field.

The two-axis magnetic structure has a magnetic flux guide in a shape ofa square ring or a circular structure, in which four gaps aresymmetrically located along a structure of the magnetic flux guide. Eachof the four gaps has a similar shape of parallelogram. Fourmagnetoresistors R₁, R₃, R₅, R₇ are placed respectively in the fourgaps, and another four magnetoresistors R₂, R₄, R₆, R₈ are placed andshielded under the magnetic flux guide. The magnetoresistors R₁, R₃, R₅,R₇ placed in the four gaps are with the length parallel to therespective edge of the four gaps; Wheatstone bridge 1 and 2 and formedfrom the eight magnetoresistors: the bridge 1 is composed of twomagnetoresistors R₁, R₃ in the gaps and another two magnetoresistors R₂,R₄ under the magnetic flux guide. The bridge 2 comprises twomagnetoresistors R₅, R₇ in the gaps and another two magnetoresistors R₆,R₈ under the magnetic flux guide. Bridge 1 is used to measure theX-component of the external magnetic field, while bridge 2 is formeasuring the Y-component of the external magnetic field.

The single-axis sensing structure is with a push-pull Wheatstoneconfiguration comprising a flux guide in a rectangular shape wheremagnetoresistors R₉ and R₁₁ are placed geometrically in the oppositeside of the flux guide relative to magnetoresistors R₁₀ and R₁₂. Themagnetoresistors are capable of sensing the X-component of the magneticfringe field at a proximity of the flux guide induced by the componentof magnetic field along the Z axis. The X-component of the magneticfringe fields generated on opposite sides of the flux guide aredirectionally antiparallel, leading to a push-pull sensing bridge thatis capable of producing a differential output proportional to theexternal magnetic component along the Z axis.

The single-axis sensing structure is placed inside or outside of theannular or semi annular magnetic guiding structure within the two-axismagnetic sensing structure. The substrate is silicon substrate, sapphiresubstrate glass substrate or polymer substrate. The magnetoresistors aremade from materials of Anisotropic Magnetoresistance (AMR), the giantmagnetoresistance (GMR) or the tunneling magnetoresistance (TMR). Theflux guides are composed of soft magnetic materials. Furthermore, thesensing structure could be integrated together with semiconductorcircuits in an IC compatible wafer process. In addition, the Wheatstonebridges could be composed of either four resistors forming a full-bridgestructure or two resistors forming a half-bridge structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an overall structure according to afirst embodiment of the present invention.

FIG. 2 is a schematic diagram of the overall structure according to asecond embodiment of the present invention.

FIG. 3 is schematic diagrams exhibiting two Wheatstone bridges withinthe two-axis sensing structure.

FIG. 4 is a simulated output for X- and Y-magnetic field componentsverses an angle between the X axis and the applied rotating magneticfield within two-axis sensing structure.

FIG. 5 is a schematic diagram of the Wheatstone bridge within thesingle-axis magnetic sensing structure.

FIG. 6 is a simulated output verses the Z-axis component of appliedmagnetic field in the single-axis magnetic sensing structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A three-axis magnetic sensor, comprises: a substrate, a two-axismagnetic sensing structure consisting of two Wheatstone bridgeconfigurations within an annular or semi annular magnetic flux-guidingstructure, and a single-axis sensing structure consisting of a push-pullWheatstone bridge configuration with a flux guide to generate fringefield proportional to vertical component of magnetic field signal. Thesingle-axis structure is placed outside of the annular magnetic fluxguide of the two-axis magnetic sensing structure.

The two-axis magnetic sensing structure is set on the substrate, and theexternal frame of the flux guide 1 is a shape of a square ring or acircular structure. The flux guide is divided into four segments by fourgaps. The four gaps of the shielding structure have shapes ofparallelogram (with the sharp angles in the range of above 0 degree andbelow 90 degree). Four sensitive magnetoresistors R₁, R₃, R₅, R₇ placedin the four gaps, and another four shielded magnetoresistors R₂, R₄, R₆,R₈ are placed under the magnetic flux guide segments. Themagnetoresistors have a shape of parallelogram or square or rectanglewith two sides parallel to the edge of the gaps. The eight resistorsmake up two Wheatstone bridge 1 and 2; wherein bridge 1 is used tomeasure the magnetic component of the magnetic field along the X-axis,and bridge 2 is used to measure the magnetic component of the magneticfield along the Y-axis. The bridge 1 comprises two magnetoresistors R₁,R₃ in the gaps that is capable of sensing the X-axis magnetic componentand another two magnetoresistors R₂, R₄ under the magnetic flux guide.The bridge 2 comprises two magnetoresistors R₅, R₇ in the gaps that iscapable of sensing the Y-axis magnetic component and another twoshielded magnetoresistors R₆, R₈ under the magnetic flux guide.

The single-axis sensing structure is with a push-pull Wheatstoneconfiguration comprising a flux guide in a rectangular shape. Thepush-pull Wheatstone bridge consists of four magnetoresistors, in whichtwo magnetoresistors R₉ and R₁₁ are placed symmetrically to the oppositeside of the flux guide relative to the other two magnetoresistors R₁₀and R₁₂. The magnetoresistors is capable of sensing the X-axis componentof the magnetic fringe field at the proximity of the flux guide inducedby the component of magnetic field along the Z axis. The X-axiscomponent of the magnetic fringe fields generated on the opposite sidesof the flux guide are directionally antiparallel, leading to a push-pullsensing bridge that is capable of producing a differential outputproportional to the external magnetic component along the Z axis.

Magnetic flux guide is usually made of soft magnetic material of highpermeability, such as nickel iron, iron silicon alloy (silicon steelsheet) or various soft ferrite materials.

As shown in FIG. 1 , in the preferred embodiment 1, the single-axismagnetic sensor is placed outside the flux guide F1 of the two-axialmagnetic sensing structure.

As shown in FIG. 2 , in the preferred embodiment 2, the single axismagnetic sensor is placed inside the flux guide F1 of two-axis magneticsensing structure, which is capable of greatly reducing the interferenceof the horizontal magnetic field to the single-axis magnetic sensingstructure.

For above mentioned preferred embodiments, the two-axis magnetic sensingstructure consists of eight magnetic sensitive resistors, the flux guideF1 has a square ring structure with four gaps, with one magnetoresistorplaced in each gap, and another four magnetoresistors placed under thefour flux guide segments. The eight resistors make up two Wheatstonebridge 1 and bridge 2. As shown in FIG. 3 , the bridge 1 is composed oftwo magnetoresistors R₁, R₃ in the gaps that is capable of sensing theX-axis magnetic component and two magnetoresistors R₂, R₄ shielded bythe magnetic flux guide. The bridge 2 comprises two sensitivemagnetoresistors R₅, R₇ in the gaps that is capable of sensing theY-axis magnetic component and two magnetoresistors R₆, R₈ under themagnetic flux guide. The two Wheatstone bridge measures the magneticcomponents of the external magnetic field along the X-axis and Y-axisrespectively. The output simulation curves of the two Wheatstone bridgesare shown in FIG. 4 . The two output simulation curves are typicalcosine curves with a phase angle difference of about 90 degrees.

For above mentioned preferred embodiments, the single-axis magneticsensing structures consist of four magnetic sensitive resistors. Theflux guide F2 has a shape of square or rectangle with four resistorsplaced symmetrically on two sides of the flux guide F2. The twomagnetoresistors R₉ and R₁₁ are geometrically placed on one side of theflux guide, while the other two magnetoresistors R₁₀ and R₁₂ are placedon the other side. The external magnetic component along the Z axiscould induce an X-axis component of the magnetic fringe field at theproximity of the flux guide, and the directions of the X-axis componentsare anti-parallel on both opposite sides of the flux guide. As shown inFIG. 5 .

As shown in FIG. 6 , the simulation curve shows that the X-axiscomponent of excited fringe field generated by the Z-axis component ofthe external magnetic field varies with the distance away from thecenter of the flux guide F2. It is noted that the X-axis components ofexcited fringe fields on two sides of the flux guide F2 exhibit the sameamplitude symmetrically with the opposite field direction. Therefore, ifthere is an external magnetic field with the Z-axis components, themagnetoresistances of the R₉ and R₁₁ will increase/decrease, while themagnetoresistances of R₁₀ and R₁₂ will decrease/increase in a push-pullmode, producing a differential output that is proportional to the Z-axiscomponent of the external magnetic field. As for the configuration ofthe preferred embodiment 2 shown in FIG. 2 , there is another advantagein that the flux guide F1 could shield the influence of the X-axiscomponent of the external magnetic field on the inside single-axissensing structure, which measures the Z-axis component of the externalfield.

For those skilled in the art, it is clear that the invention technologyis not limited to the details of the above exemplary embodiments, andthat the invention technology can be realized in other specific formswithout departing from the spirit or basic characteristics of theinvention technology. Therefore, at any point, an example should beregarded as exemplary and unrestrictive, and the scope of the inventiontechnology is defined by the appended claims rather than the abovedescription, so that changes in the meaning and scope of the equivalentelements of the claim are included in the technology of the invention.Any appended map mark in the claim shall not be regarded as a limitationof the claims.

What is claimed is:
 1. A three-axis magnetic sensor apparatuscomprising: a substrate, a two-axis magnetic sensing structureconsisting two shielded Wheatstone bridge configurations in conjunctionwith a first magnetic flux guide which is annular or semi annular, and asingle-axis sensing structure consisting a push-pull Wheatstone bridgeconfiguration in conjunction with a second magnetic flux guide that iscapable of generating a fringe field whose horizontal component isproportional to vertical component of a magnetic field; wherein thesecond magnetic flux guide in a rectangular shape where twomagnetoresistors of the push-pull Wheatstone bridge configuration aregeometrically placed in the opposite side of the second magnetic fluxguide relative to the other two magnetoresistors of the push-pullWheatstone bridge configuration; wherein the two-axis magnetic sensingstructure with two shielded Wheatstone bridge configurations and asingle-axis structure with a push-pull Wheatstone bridge configurationare processed together into a single chip, and is for measuring anX-component, a Y-component and a Z-component of an external magneticfield; wherein the two-axis magnetic structure has a first magnetic fluxguide in a shape of a square ring or a circular structure, in which fourgaps are symmetrically located along a structure of the first magneticflux guide; wherein each of the four gaps has a similar shape ofparallelogram; four magnetoresistors R₁, R₃, R₅, R₇ are placedrespectively in the four gaps, and another four magnetoresistors R₂, R₄,R₆, R₈ are placed an d shielded under the first magnetic flux guide; themagnetoresistors (R₁, R₃, R₅, R₇ placed in the four gaps are with thelength parallel to the respective edge of the four gaps; Wheatstonebridge 1 and 2 and formed from the eight magnetoresistors: the bridge 1comprises two magnetoresistors R₁, R₃ in the gaps and another twomagnetoresistors R₂, R₄ under the first magnetic flux guide; the bridge2 comprises two magnetoresistors R₅, R₇ in the gaps and another twomagnetoresistors R₆, R₈ under the first magnetic flux guide; bridge 1 isused to measure the X-component of the external magnetic field, whilebridge 2 is for measuring the Y-component of the external magneticfield.
 2. The three-axis magnetic sensor apparatus of claim 1, whereinthe single-axis sensing structure is with the push-pull Wheatstoneconfiguration comprising the second magnetic flux guide in a rectangularshape where magnetoresistors R₉ and R₁₁ are geometrically placed in theopposite side of the second magnetic flux guide relative tomagnetoresistors R₁₀ and R₁₂; the magnetoresistors are capable ofsensing the X-component of the magnetic fringe field at a proximity ofthe second magnetic flux guide induced by the component of magneticfield along the Z axis; the X-component of the magnetic fringe fieldsgenerated on opposite sides of the second magnetic flux guide are indirectionally antiparallel, leading to a push-pull sensing bridge thatis capable of producing a differential output proportional to theexternal magnetic component along the Z axis.
 3. The three-axis magneticsensor apparatus of claim 1, wherein the single-axis sensing structureis placed inside or outside of the annular or semi annular magneticguiding structure within the two-axis magnetic sensing structure.
 4. Thethree-axis magnetic sensor apparatus of claim 1, wherein the substrateis a silicon substrate, a sapphire substrate, a glass substrate or apolymer substrate.
 5. The three-axis magnetic sensor apparatus of claim1, wherein the magnetoresistors are made from materials of AnisotropicMagnetoresistance (AMR), giant magnetoresistance (GMR) or tunnelingmagnetoresistance (TMR).
 6. The three-axis magnetic sensor apparatus ofclaim 1, wherein both the first magnetic flux guide and the secondmagnetic flux guide are composed of soft magnetic materials.
 7. Thethree-axis magnetic sensor apparatus of claim 1, wherein the sensingstructure is integrated together with semiconductor circuits in an ICcompatible wafer process.
 8. The three-axis magnetic sensor apparatus ofclaim 1, wherein the Wheatstone bridges is composed of either fourresistors forming a full-bridge structure or two resistors forming ahalf-bridge structure.